It is well known that natural and synthetic rubbers ordinarily must be mixed or "compouned", with vulcanizing agents, plasticizers, extenders, fillers, pigments and the like, so that the rubber can be cured or vulcanized in a mold to form useful articles. It has often been found necessary to include "processing aids" in the rubber compound prior to molding and curing. These processing aids are primarily intended to improve the mixing of the ingredients of the rubber compound, the flowability of the rubber during processing, and the mold or mill release properties of the rubber, without seriously adversely affecting the properties of the cured rubber. Indeed, to the extent they facilitate uniform dispersion of compound ingredients, they can improve the physical properties of the cured rubber, and by imparting improved flow and mold release properties they can improve the appearance of the molded, cured rubber.
Among the processing aids which have been employed are petroleum products referred to as "petrolatum". As is well known, petrolatum is a smooth, semisolid (at room temperature (77.degree. F.)) blend of mineral oil with waxes crystallized from the residual type of petroleum lubricating oil. Typically, the wax molecules contain 30-70 carbon atoms and are largely straight chains with a few branches or naphthene rings. The waxes ordinarily are in the form of microneedles which hold the oil in a gel. Petrolatum is easily deformed under slight pressure at room temperature, melts in a range of from about 110.degree.-175.degree. F., and molten petrolatum is characterized by high viscosity (i.e., from about 60 to about 120 Saybolt Units at 210.degree. F.).
Petrolatum has been used as a rubber processing aid primarily to improve mold and mill release properties of rubber compounds and to improve the flow properties of rubber during compounding. For these purposes, it ordinarily was employed in small amounts, typically from about 1/2 to about 5 weight percent, based upon the total rubber compound. However, because of its semisolid nature, it is difficult to employ. It is difficult to remove from containers, to accurately measure the quantity to be added and be certain that the petrolatum is uniformly distributed throughout the compound in the intended proportion.